Space vehicles often carry sensors that must be kept very cold, and the lifetime of the sensors is often limited by the cryocooler, or low-temperature refrigerator. For example, the useful life of far-infrared sensors on surveillance satellites, which are maintained at a temperature of about 10.degree. K., is presently limited by the lifetime of the cryocooler. The useful life of the cooling system can be extended by using redundant cryocoolers, with a first cryocooler thermally coupled to the sensor and the inactive backup cryocooler thermally isolated therefrom until needed. Heat switches for establishing such thermal connection or isolation have not been of high efficiency or high reliability. Reliable operation may be required over extended periods of time, such as a minimum of five to ten years. Mechanically actuated heat switches have been proven unreliable at cryogenic temperatures and further require large contact force. Magneto-resistive heat switches are, except at very low temperatures, of very low efficiency. Heat switches operated by the heat pipe principle usually require a long response time. Gas gap heat switches, such as described in U.S. Pat. No. 4,366,680 can provide reliable thermal connection and isolation, except that they have previously required heating or cooling coils to control the temperature of the sorption pumps that operate the heat switches, and also require control and power sources for operating such heating or cooling coils. Prior gas gap heat switches such as described in U.S. Pat. No. 4,366,680 had low heat transfer capacity and low heat switch ratios. A redundant refrigeration system which enabled the use of gas gap heat switches, and which provided efficient switches of that type, while avoiding the previous disadvantages in the use of such heat switches, would be of considerable value.